Displacement measurement device and defect detection device

Abstract

A displacement measurement deviceis provided with: a laser light sourcefor emitting laser light to a measurement area R of a measurement target object S; a focusing optical system (the beam splitter, the first reflecting mirror, the condenser lens) having a front focal point in the measurement area R and a rear focal point on a predetermined imaging surface (the detection surface); a non-focusing optical system (the beam splitter, the diffuser, the second reflecting mirror, and the condenser lens) in which light from a measurement area R of a correspondence point in the measurement area corresponding to each point of the imaging surface with respect to the focusing optical system is incident on the point of the imaging surface; and a photodetector (image sensor) configured to detect light intensity on the imaging surface for each point. Thus, corresponding to each of a large number of points in the measurement area R, main reflected light reflected at the point and reference light reflected at the surrounding range of the point are incident on each of a large number of points in the imaging surface, and the main reflected light and the reference light interfere at a large number of points in the imaging surface. Thus, an interference pattern is obtained.